Charged particle detection system

ABSTRACT

A scintillator assembly including an entrance surface for receiving charged particles into the scintillator assembly, the charged particles including first charged particles at a first energy level and second charged particles at a second energy level. A first scintillator structure configured for receiving the first charged particles and generating a corresponding first signal formed of first photons with a first wavelength of λ1, a second scintillator structure configured for receiving the second charged particles and generating a corresponding second signal of second photons with a second wavelength of λ2, and an emitting surface for egress of a combined signal from the scintillator assembly, the combined signal including the first and second photons, and at least one beam splitter for receiving the combined signal and separating the combined signal to first and second photons.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a divisional of and claims priority to and thebenefit of all of: U.S. patent application Ser. No. 16/810,879, filedMay 6, 2020 and entitled “CHARGED PARTICLE DETECTION SYSTEM”, whichclaims priority benefit from U.S. Provisional Application No.62/814,604, filed Mar. 6, 2019, entitled “MULTILAYER SCINTILLATORASSEMBLY”. The disclosures of each of the above applications areincorporated herein by reference in their entireties.

TECHNICAL FIELD

This application relates generally to charged particle detection systemsand particularly to charged particle detection systems comprisingmultilayer scintillators.

BACKGROUND

Charged particle beam systems employed for inspection and/or imagingpurposes typically generate a primary beam, of electrons or ions, whichis focused onto the surface of a specimen by a charged particle beamcolumn. The detection process generally involves the collection ofdifferent types of charged particles, such as, inter alia, secondaryelectrons (SE), secondary ions (SI), backscattered electrons (BSE)and/or backscattered ions (BSI), sputtered ions, etc. which are emittedfrom the specimen as a result of the interaction of the primary chargedparticle beam with the specimen. Additional types of charged particlesinclude tertiary electrons (SE3) and/or tertiary ions (SI3) emitted fromany surface within the detection system (other than the surface of thespecimen) due to impingement of backscattered electrons and/orbackscattered ions, neutral atoms or other particles thereon.

In order to inspect or form an image of the specimen, it is advantagesto selectively detect charged particles produced due to operation of acharged particle beam column irradiating a specimen.

The different types of charged particles possess different energylevels. For a non-limiting example, a first type of charged particlescomprises the secondary electrons (SEs), which have low energiesspanning from several eV up to several tens of eV, such as up to 50 eV.A second type of charged particles comprises the backscattered electrons(BSEs) which have higher energies up to the initial primary beam energy(elastic interaction), that span from 50 eV or even hundreds of eV up toseveral tens of keV. Due to the energy level differences, the differenttypes of charged particles are emitted from different regions within anirradiated specimen. BSEs come from deeper regions of the specimen,whereas SE originate from surface regions. Thus, the BSEs and the SEscarry different types of information. The different type of informationaffects the resultant image of the specimen. BSE images show highsensitivity to differences in the atomic number. The higher the atomicnumber, the brighter the material appears in the image. SE imaging canprovide more detailed surface information.

Charged particle detectors are utilized to detect the charged particlesemitted from the specimen. Scintillators may be deployed in the chargedparticle detectors to transfer charged particle energy into a pluralityof photons with a specific wavelength. Different types of chargedparticles may strike the scintillator. Exemplary systems utilizing thecharged particle detectors comprise microscopy systems, such as ScanningElectrons Microscopes (SEMs). Conventional particle detectors detect thedifferent types of charged particles in discrete, subsequent detectionevents, referred to as “grabs”. For example, initially the chargedparticle detector will be arranged to detect a SE at a first detectionevent, namely a first grab, and process the SE data into a first image.Thereafter in a second detection event, namely a second grab, will thecharged particle detector be arranged to detect the BSEs and process theBSE data into a second image.

SUMMARY

The following summary of the invention is included in order to provide abasic understanding of some aspects and features of the disclosure. Thissummary is not an extensive overview of the disclosure and as such it isnot intended to particularly identify key or critical elements of thedisclosure or to delineate the scope of the disclosure. Its sole purposeis to present some concepts of the disclosure in a simplified form as aprelude to the more detailed description that is presented below.

There is provided in accordance with some embodiments, a chargedparticle detection system configured for detecting charged particles ofdifferent energy levels emitted from a specimen, which is impinged uponby a particle beam. In a non-limiting example the charged particlescomprise SEs and BSEs. The SEs are emitted out of a more superficiallayer of the specimen while the BSEs come from deeper regions into thespecimen, according to initial penetration depth of the primary particlebeam. The charged particle detection system comprises a multilayerscintillator assembly. The multilayer scintillator assembly comprises atleast two active layers. The charged particle energies are tunedcorrespondingly by use of proper bias of the multilayer scintillatorassembly to attract the charged particles thereto, and accelerate themif required. Due to their lower energy, the SEs should reach the firstscintillator layer, while higher energy BSEs should mostly reach thedeeper second scintillator layer. The first layer generates lightphotons with the wavelength λ1, while the second layer generates photonswith the wavelength λ2.

The signals from the two layers carry different image information, andnow they can be separated according to their corresponding wavelengths.One non-limiting method to implement this separation is using a dichroicfilter, which can reflect shorter wavelengths, but transmit longerwavelengths (above a predefined threshold) or vice versa.

There is thus provided in accordance with an embodiment of the presentdisclosure, a particle detection system including a multilayerscintillator assembly including at least two scintillator layers,wherein a first scintillator layer is configured to generate a firstsignal of photons with a first wavelength λ1 in response to a chargedparticle of a first type impinging thereon, and a second scintillatorlayer is configured to generate a second signal of photons with a secondwavelength λ2 in response to a charged particle of a second typeimpinging thereon, and a beam splitter for separating the first signalfrom the second signal.

In some embodiments, the first scintillator layer overlies or underliesthe second scintillator layer. In some embodiments, the beam splitter isengaged at least with a first photomultiplier device for receiving thephotons with the first wavelength λ1 and generating first photoelectronstherefrom, and a second photomultiplier device for receiving the photonswith the second wavelength λ2 and generating second photoelectronstherefrom.

In some embodiments, the beam splitter is engaged with the firstphotomultiplier device via a first light guide and the beam splitter isengaged with the second photomultiplier device via a second light guide.

In some embodiments, at least one of the first and secondphotomultiplier devices is a photomultiplier tube (PMT). In someembodiments, the particle detection system further include at least afirst and second pre-amplifier for receiving respective first and secondphotoelectrons and amplifying the first and second photoelectrons, atleast a first and second digitizing device for digitizing the respectiveamplified first and second photoelectrons, and at least a first andsecond processor for processing the respective digitized first andsecond photoelectrons, thereby producing a first image based on thefirst photoelectrons and a second image based on the secondphotoelectrons.

In some embodiments, the beam splitter includes a dichroic filter. Insome embodiments, the multilayer scintillator assembly is segmented intotwo or more segments. In some embodiments, each of the two or moresegments is engaged with a corresponding beam splitter.

There is thus provided in accordance with an embodiment of the presentdisclosure, a scintillator assembly including an entrance surface forreceiving incident electrons into the scintillator assembly, theincident electrons including at least first incident electrons at afirst energy level and second incident electrons at a second energylevel, at least a first scintillator structure configured for receivingthe first incident electrons and generating a corresponding first signalformed of photons with a first wavelength of λ1, at least a secondscintillator structure configured for receiving the second incidentelectrons and generating a corresponding second signal of photons with asecond wavelength of λ2, and an emitting surface for egress of acombined signal from the scintillator assembly, the combined signalincluding the photons with the first wavelength λ1 and the photons withthe second wavelength λ2, and at least one beam splitter for receivingthe combined signal and separating the combined signal to photons withthe first wavelength λ1 and the photons with the second wavelength λ2.

There is thus provided in accordance with an embodiment of the presentdisclosure, a signal separation system for distinguishing between atleast a first type of charged particle and a second type of chargedparticle emitted from a specimen, including a convertor assemblyincluding at least a first layer configured to emit, in response toimpingement of the first type of charged particle on the first layer, afirst signal containing a first type of image information, and a secondlayer configured to emit, in response to impingement of the second typeof charged particle on the second layer, a second signal containing asecond type of image information, the first and second signals areemitted as a combined signal from the convertor assembly, and a signalseparator assembly configured to receive the combined signal andseparate the first signal from the second signal.

In some embodiments, the first signal is emitted at a firstpredetermined wavelength and the second signal is emitted at a secondpredetermined wavelength. In some embodiments, the convertor assemblyincludes a multilayer scintillator assembly including the first layerwhich includes a first scintillating layer and the second layer whichincludes a second scintillating layer. In some embodiments, the firsttype of charged particle include at least one of secondary electrons(SEs) and secondary ions (SIs) and the second type of charged particleinclude at least one of backscattered electrons (BSEs) and backscatteredions (BSIs). In some embodiments, the first and second signal arereceived synchronously by the signal separator. In some embodiments,wherein following separation of the first signal from the second signalby the signal separator, the separated first signal is directed to afirst image processor for producing a first image containing the firstimage information and the separated second signal is directed to asecond image processor for producing a second image containing thesecond image information. In some embodiments, the first image and thesecond image show image information captured synchronously. In someembodiments, the signal separation system is positions within amicroscopy system.

There is thus provided in accordance with an embodiment of the presentdisclosure, a method for separating signals for distinguishing betweenat least a first type of charged particle and a second type of chargedparticle emitted from a specimen, including irradiating a specimen witha primary beam for emitting at least the first type of charged particleand the second type of charged particle impinging a first layer of aconvertor assembly configured to emit, in response to impingement of thefirst type of charged particle on the first layer, a first signalcontaining a first type of image information, impinging a second layerof the convertor assembly configured to emit, in response to impingementof the second type of charged particle on the second layer, a secondsignal containing a second type of image information, wherein a combinedsignal including the first and second signal emits the convertorassembly, receiving the combined signal by a signal separator assembly,and separating the combined signal by the signal separator assembly intoat least the first signal and the second signal.

In some embodiments, the separated first signal is amplified by a firstphotomultiplier and processed to provide an image containing the firsttype of image information and the separated second signal is amplifiedby a second photomultiplier and processed to provide an image containingthe second type of image information.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, exemplify the embodiments of the presentinvention and, together with the description, serve to explain andillustrate principles of the invention. The drawings are intended toillustrate major features of the exemplary embodiments in a diagrammaticmanner. The drawings are not intended to depict every feature of actualembodiments nor relative dimensions of the depicted elements, and arenot drawn to scale.

FIG. 1 is a simplified pictorial illustration of a charged particledetection system constructed and operative in accordance with anembodiment of the present disclosure;

FIG. 2 is a simplified pictorial illustration of a charged particledetection system constructed and operative in accordance with anembodiment of the present disclosure;

FIG. 3 is a simplified pictorial illustration of a charged particledetection system constructed and operative in accordance with anembodiment of the present disclosure;

FIG. 4 is a simplified pictorial illustration of a charged particledetection system constructed and operative in accordance with anembodiment of the present disclosure;

FIGS. 5A and 5B are each a simplified pictorial illustration of acharged particle detection system constructed and operative inaccordance with an embodiment of the present disclosure;

FIG. 6 is a simplified pictorial illustration of a charged particledetection system constructed and operative in accordance with anembodiment of the present disclosure;

FIG. 7 is a simplified pictorial illustration of a charged particledetection system constructed and operative in accordance with anembodiment of the present disclosure; and

FIG. 8 is a simplified pictorial illustration of a charged particledetection system constructed and operative in accordance with anembodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, various aspects of the present inventionwill be described. For purposes of explanation, specific configurationsand details are arranged forth in order to provide a thoroughunderstanding of the present invention. However, it will also beapparent to one skilled in the art that the present invention may bepracticed without the specific details presented herein. Furthermore,well known features may be omitted or simplified in order not to obscurethe present invention.

FIGS. 1 and 2 are a simplified pictorial illustration of a chargedparticle detection system 100 constructed and operative in accordancewith an embodiment of the present disclosure. The charged particledetection system 100 comprises a charged particle detector 102configured for detecting charged particles of different energy levelsemitted from a specimen 106 which is impinged upon by a charged particlebeam 108 (namely the primary particle beam), generated by a particlebeam column 110 (FIG. 3). Particle beam column 110 may comprise anelectron beam column, a focused ion beam (FIB) column, a dual beamcolumn, a helium beam column or any other suitable particle beam column.In a non-limiting example the particle beam column 110 is in amicroscopy system, such as a SEM or a TEM (Transmission ElectronMicroscope) or the like. The particle beam 108 irradiates the specimen106 causing charged particle (positive/negative ion and/or electron)emission from the specimen 106. The emitted particle propagates towardsthe charged particle detector 102.

The charged particles of different energy levels may comprise, in anon-limiting example, incident charged particles. The incident chargedparticles may comprise at least first incident charged particles at afirst energy level and second incident charged particles at a secondenergy level. In the non-limiting embodiment of

FIG. 1 the first incident charged particles at a first energy levelcomprise Secondary Electrons (SEs) 114 and the second incident chargedparticles at a second energy level comprise Backscattered Electrons(BSEs) 116.

In the embodiment of FIG. 1, the SEs 114 are shown to emit from aproximal (or namely an exterior or superficial) surface 120 of thespecimen 106 relative to the beam column 110 while the BSE emit from adistal (or namely an interior or deeper) surface 122 of the specimen106.

In other embodiments, the SEs 114 and BSEs 116 may be both emitted fromthe exterior surface 120 or the interior surface 122 or alternatively,the SEs 114 may be emitted from the exterior surface 120 and BSEs 116may be emitted from the interior surface 122.

The charged particle detector 102 comprises a multilayer scintillatorassembly 130. The multilayer scintillator assembly 130 may be formedwith an entrance surface 134 for receiving the incident chargedparticles into the multilayer scintillator assembly 130.

In some embodiments, the multilayer scintillator assembly 130 may bebiased so as to attract the charged particles thereto. In a non-limitingexample, the multilayer scintillator assembly 130 is positively biased,e.g. in the range of about 6 to 12 kV, to attract the SEs 114 and BSEs116 or any other negatively charged particles and accelerate SEs 114 andBSEs 116 to higher energies. In a non limiting example, the multilayerscintillator assembly 130 may be biased in the range of 3-12 kV. In sucha case generally the SE energies will be approximately 3-12 keV, whilethe BSE energies will span in the range of the SE energy level plus 50eV to the primary particle beam energy level.

The entrance surface 134 may comprise any suitable material. In someembodiments the entrance surface 134 may comprise a reflective layer,such as comprising aluminum. The reflective layer may be used to reflectundesired, parasite light impinging upon the multilayer scintillatorassembly 130 from a location other then the specimen 106. In someembodiments, the entrance surface 134 may be formed of a conductivematerial (such as aluminum) to prevent excessive charging of themultilayer scintillator assembly 130. In some embodiments, the entrancesurface 134 may be omitted.

The multilayer scintillator assembly 130 comprises at least a firstscintillator structure 140 and a second scintillator structure 142 andmay comprise additional structures. In the embodiments of FIGS. 1 and 2,the first scintillator structure 140 is formed as a layer and underliesthe second scintillator structure 142, formed as a layer as well.

The penetration depth measures an average depth reached by the chargedarticle within the multilayer scintillator assembly 130 and is afunction of the charged particle energy and stopping power of thescintillator structure materials of 140, 142 and entrance surfacematerial 134. The stopping power is the retarding force acting on thecharged particles, due to interaction with matter, such as the first andsecond scintillator structures 140 or 142, resulting in loss of thecharged particle energy. In a non-limiting example, for electrons, thepenetration depths may range from several hundreds of nanometers forelectrons of about 5 keV (e.g. SEs) up to several microns for electronsat about 50 keV (e.g. BSEs).

In a non-limiting example, the thickness of the entrance surface 134 maybe in the range of about 10-100 nanometers, the thickness of each of thefirst and second scintillator structures 140 or 142 may be in the range100 nanometers to 10 microns, a thickness of an emitting surface 150,described hereinafter, may be about 100 microns or more. The penetrationdepth of the SEs 114 is such that it reaches within the scintillatorstructures 140 and the penetration depth of the BSEs 116 is such that itreaches within the second scintillator structure 142.

The first and second scintillator structures 140 and 142 may each beformed with a material configured to emit photons at a different,separable wavelength. In a non limiting example, the first scintillatorstructure 140 may be formed of a first material configured to emitphotons at a first predetermined wavelength while the secondscintillator structure 142 may be formed of a second material configuredto emit photons at a second wavelength, which is in the range of 2-2000nanometers (e.g. any one of 20, 50, 100, 200, 500 nanometers) greaterthan the first predetermined wavelength. In other words, the wavelengthλ2 is in the range of 2-2000 nanometers (including values and subrangestherebetween) greater than the wavelength λ1. The first and secondmaterials may comprise any scintillating material, such as GalliumNitride, Gallium Arsenide, GaAsAl. The first and second material may bedifferent or may comprise the same material, e.g. Gallium Nitride,wherein the first material remains pure and the second material is dopedor vice versa. or wherein both materials are doped to different degrees.In some embodiments, in a non-limiting example any one of the first andsecond scintillator structures 140 and 142, the entrance surface 134 andthe emitting surface 150 may comprise quantum wells.

The first scintillator structure 140 is configured for receiving thefirst incident electrons, e.g. the SEs 114. In response, the firstscintillator structure 140 generates a corresponding first signal 144formed of photons with a first wavelength of λ1, carrying first imageinformation. The second scintillator structure 142 is configured forreceiving the second incident electrons, e.g. the BSEs 116. In response,the second scintillator structure 142 generates a corresponding secondsignal 146 formed of photons with a second wavelength of λ2, carryingsecond image information.

Though each scintillator structure emits a different signal, the photons148 egressing from an emitting surface 150 of the multilayerscintillator assembly 130, comprise a combined signal of both the firstsignal λ1 and the second signal λ2 indistinguishably when egressing froman emitting surface 150. The signals may be separated by a signalseparator assembly, as will be further described.

The emitting surface 150 may be configured in any suitable manner andmay be formed of any suitable material, such as a transparent material,e.g. glass. The emitting surface 150 may serve as a substrate to themultilayer scintillator assembly 130 for providing mechanical stability.

The first and second scintillator structures 140 and 142, entrancesurface 134 and the substrate 1050 are not shown to scale.

As seen in FIG. 2, the charged particle detection system 100 maycomprise at least one signal processing subassembly 152 comprising atleast one signal separator assembly 154, e.g. a beam splitter, forreceiving the egressed photons 148 from the multilayer scintillatorassembly 130 and further optically separating the photons 144 with thefirst wavelength λ1 from the photons 146 with the second wavelength λ2.Namely, in the embodiment of FIGS. 1 and 2, the beam splitter 154separates the first signal generated by the SEs 114 from the secondsignal generated by the BSEs 116.

The signal separator assembly 154 may comprise any device for opticallyseparating the combined signal, comprising of two different wavelengthsλ1 and λ2, and emitted from the multilayer scintillator assembly 130, asa result of the first signal 144 and the second signal 146.

In some embodiments, the signal separator assembly 154 comprising thebeam splitter may comprise a dichroic filter, which can reflect shorterwavelengths, but transmit longer wavelengths (above a predefinedthreshold). In some embodiments, the beam splitter 154 may comprise athin-film filter, absorbing filter, an interference filter or any devicethat is deployed to selectively pass light of a small range of colorswhile reflecting other colors or any other type of signal or informationor vice versa. In another embodiment, the signal separator assembly 154may comprise a position sensitive filters, that can be moved by precisemotors. A pair of position sensitive filters (low pass and high pass)activated by precise motors or actuators can be also used for wavelengthseparation.

The signal processing subassembly 152 may comprise a light guide 156,formed in any suitable shape. Light guide 156 may be optically coupledto the multilayer scintillator assembly 130, so photons of the combinedsignal 148 propagate thereto. Then, the photons of the combined signal148 arrives at the beam splitter 154, which may be mechanically attachedor adhered to the light guide 156. In a non-limiting example, the firstsignal 144 is reflected from the beam splitter 154 and continues topropagate in a 90 degree, or at any other suitable angle, at a firstbranch 158 of the light guide 156 at a bifurcation junction 160 thereof.Subsequently, the first light guide branch 158 is coupled to aphoto-cathode (PC) of a first photomultiplier tube (PMT1) 162 convertingphotons into first photoelectrons. The PMT1 162 amplifies thephotoelectron signal to the level required to feed a pre-amplifier(Pre-amp 1) unit 164. Thereafter, at the output of the Pre-amp1 164, thesignal may be digitized and processed by an Image Channel1 166 toprovide an image containing the first type of image information in thedigital form or by any other suitable means. In some embodiments, anyother devices for providing an amplified signal and electrical output,such as photomultipliers, may be provided, such as in a non-limitingexample a Multi-Pixel Photon Counter (MPPC), also known as a siliconphotomultiplier (SiPM).

The second signal 146 is transmitted by the beam splitter 154, andoptically coupled to a second branch 168 of the light guide 156. Thelight guide 156 may be formed as a manifold with a base 170 bifurcatinginto at least two branches 158 and 168. The light guide 156 may beformed as a monolith unit or may comprise a plurality of light guidesmechanically and optically adhered to each other at any angle orconfiguration. As seen in FIG. 2, the second branch 168 is mechanicallyattached or glued to the beam splitter 154 at the base 170.Subsequently, the second light guide branch 168 is coupled to a secondphoto-cathode (PC) of a second photomultiplier (PMT2) 174 convertingphotons into second photoelectrons. The PMT2 174 amplifies thephotoelectron signal to the level required to feed a secondpre-amplifier (Pre-amp 2) 176. Subsequently, at the output of thePre-amp 2 176, the signal is digitized and processed by a second ImageChannel2 178 to provide an image containing the second type of imageinformation. Both channels may be independently controlled by separatePMTs, pre-amps, and video channel electronics.

In the embodiment of FIGS. 1 and 2 the first or second respective PMT162 or 174 is deployed for augmenting the incoming light signal and forconverting the photons to electrons. It is appreciated that any othersuitable device for converting photons to electrons and/or augmentingthe signal may be used, such as in a non-limiting example, an avalanchephoto diode or a PIN diode, or MPCC/SiPM.

As seen in FIG. 3, the charged particle detection system 100 may bedeployed in a scanning electron microscope (SEM) based tool (CDSEM,DRSEM, e-beam inspection, lab SEM, etc.). A SEM 200 comprises theparticle beam column 110 for generating the electron beam 108 whichirradiates the specimen 106. The charged particle detection system 100is positioned within the SEM 200. As seen in FIG. 3, the multilayerscintillator assembly 130 may be formed with a central aperture 220 toallow the beam 108 to propagate therethrough to the specimen 106.Alternatively the multilayer scintillator assembly 130 may not includethe aperture and may be positioned offset the electron beam 108 (notshown). In this case, the primary electrons and SE and BSE electronsshould be separated by certain distribution of electric and magneticfields within the charged particle detection system 100. In the systemcomprising a TEM 350 (FIG. 7) the aperture 220 may be obviated.

As can be seen from FIG. 1-3, the charged particle detection system 100enables simultaneous imaging of SEs 114 and BSEs 116, or any otherdifferent types of charged particles, with subsequent separation ofsignals according to their optical wavelength by the signal separatorassembly 154.

The charged particle detection system 100 is greatly advantageous.

In a conventional charged particle detection system 100 comprising asingle layer scintillator, one would obtain a mixed signal 148 of theSEs 114 and BSEs 116 and there is no manner in which the analyst candistinguish between depths within the specimen 106. In other words, SE114 and BSE 116 contrast will be mixed up within the same image, makinganalyzing information from different layers of the specimen 106, acomplicated task. This mixed image based on the mixed signal 148 can behardly analyzed due to low contrast of BSE 116 on the high background ofSE signal 114. In some cases, SE 114 contrast can deteriorate due topresence of considerable amount of BSEs 116. As a result, theconventional type of scintillator detector would force an analyst toperform double grab measurements with changing SEM conditions betweenthe grabs. The SEM (or TEM) conditions may refer to the SEM operatingconditions, such as the setting of the primary beam (108) energy, theprimary beam current and the like.

One grab would be arranged to maximize BSE contrasts, while another grabwould be arranged optimal for SE contrasts. Double grab method isinferior for measuring overlay of the specimen 106 layers. The overlaymay be defined as the lateral and/or longitudinal displacement degree(i.e. shift) of the specimen layers in respect to each other. In the artof semiconductor wafers the shift of the layers above a predetermineddisplacement may render the wafer in operable. Thus the overlaymeasurement is significant. Measuring the overlay during a single,simultaneous grab is advantageous. Besides yielding higher precisionoverlay measurement, measuring the overlay during a single grab isquicker and thus more cost effective.

The charged particle detection system 100 enables single grabmeasurement without a need to separate between BSE 116 and SE 114contrasts by changing SEM (or TEM) conditions between grabs.

The charged particle detection system 100 enable inherent decoupling ofBSE 116 and SE 114 information acquired in the same single grab in theSEM 200. Therefore, this method and apparatus improves the SEM overlaymeasurement MAM (move, acquire, measure) time and throughput, shorteningthe gap between SEM and optical overlay measurement performance.Decoupling between BSE and SE information, obtained in the same grab,should also improve other overlay measurement characteristics. Forexample, precision and matching of the measurement should be improveddue to better image contrasts for both SE and BSE images. In otherwords, the charged particle detection system 100 enables distinguishingimage information relating to the SEs 114 from image informationrelating the BSEs 116. Furthermore, since the BSEs penetrate a deeperlayer in the specimen 106 than the SEs 114, the first and second imageinformation obtained simultaneously at the same grab can be indicativeof the depth within the specimen 106.

Moreover, measuring overlays in two successive grabs (i.e. double graboverlay measurement) unavoidably suffers from a system drift between thetwo grabs. As a result, SE and BSE images are shifted relative to eachother. This deteriorates overlay measurement precision, matching, andaccuracy. The method of the present disclosure is superior in terms ofmeasurement precision, matching, accuracy, and throughput, at the sametime.

In some embodiments, as seen in FIG. 4, the multilayer scintillatorassembly 130 may be configured such that the first scintillatorstructure 140 and the second scintillator structure 142 are positionedlaterally adjacent thereto, such as in a tiled configuration, forexample. It is appreciated that multilayer scintillator assembly 130 maycomprise any suitable configuration.

The charged particle detection system 100 may be secured within achamber of the SEM 200 or any other beam system in any suitable manner.In one embodiment, as seen in FIG. 5A, the charged particle detectionsystem 100 may be positioned within a supporting frame 300 comprisingsupporting beams 302. In another exemplary embodiment as seen in FIG.5B, the charged particle detection system 100 is secured by a pluralityof clamps or a single clamp 310.

As seen in FIG. 6, in some embodiments, the multilayer scintillatorassembly 130 may be segmented into at least two segments 320 and 322 ormore. Each segment may be equipped with its signal processingsubassembly 152 including at least: a signal separator assembly 154, alight guide 156, a PMT 162 or other signal amplifier, pre-amplifier unit164 and an image channel 166 (FIG. 2). Segmenting the multilayerscintillator assembly 130 allows for detecting the spatial location of asignal within the specimen 106. For example, a charged particle emittedfrom a left side portion 326 of the specimen 106 will reach thecorresponding left segment 320 of the multilayer scintillator assembly130. It is therefore known that an image produced by the signalprocessing subassembly 152 of the left segment is originated from theleft side portion 326 of the specimen 106. In the embodiment of FIG. 6,the segments 320 and 322 may be segmented angularly into two or moreslices. It is appreciated that the multilayer scintillator assembly 130may be segmented in any suitable manner, such as concentrically, asshown in FIG. 8 Turning to FIG. 7, it is seen that the charged particledetection system 100 may be positioned within a TEM 350 or any othersystem comprising a particle beam column 110. In the TEM 350 theparticle beam 108 is transmitted through the specimen 106. Accordingly,the charged particle detection system 100 may be positioned to underliethe specimen 106, such that the specimen 106 is intermediate the chargedparticle detection system 100 and the particle beam column 110. In FIG.7 the charged particle detection system 100 is shown to be positionedupside down relative to the charged particle detection system 100position in FIGS. 1-6.

As seen in FIG. 8, the multilayer scintillator assembly 130 may besegmented concentrically into a least an inner segment 340 and an outersegment 344 forming rings. This segment arrangement allows operating theTEM 350 in an imaging and diffraction mode to receive a correspondingrespective bright field image from the inner segment 340 and a darkfield image from the outer segment 344 at the same time and therefore adark field image and a bright field image may be produced in the samegrab.

It is appreciated that the concentrically segmented multilayerscintillator assembly of FIG. 8 can be employed within a SEM 200.

It is appreciated that the signal processing subassembly 152 of FIGS.1-8 may comprise any suitable number of signal separator assemblies 154,light guides 156 and PMTs. Though in FIGS. 1-8 the signal processingsubassembly 152 is shown to comprise two signal separator assemblies154, light guides 156 and PMTs, a single signal separator assemblies154, light guide 156 and PMT may be provided, as well as more than twosignal separator assemblies 154, light guides 156 and PMTs.

In some embodiments, there may be provided a signal separation systemfor distinguishing between at least a first type of charged particle(e.g. an SE 114) and a second type of charged particle (e.g. a BSE 116)emitted from the specimen 106, comprising a convertor assembly (e.g. themultilayer scintillator assembly 130) comprising at least a first layerconfigured to emit, in response to impingement of the first type ofcharged particle on the first layer, a first signal containing a firsttype of image information and a second layer configured to emit, inresponse to impingement of the second type of charged particle on thesecond layer, a second signal containing a second type of imageinformation. The first and second signal are emitted as a combinedsignal from the convertor assembly and a signal separator assembly 154configured to receive the combined signal and separate the first signalfrom the second signal.

It is appreciated that the charged particles are described herein ascomprising SEs 114 and BSEs 116, yet is appreciated that the system andmethod of the disclosure are applicable to any charged particles, suchas in a non-limiting example, SIs, BSIs, SE3, SI3, sputtered ions andthe like.

While various inventive embodiments have been described and illustratedherein, those of ordinary skill in the art will readily envision avariety of other means and/or structures for performing the functionand/or obtaining the results and/or one or more of the advantagesdescribed herein, and each of such variations and/or modifications isdeemed to be within the scope of the inventive embodiments describedherein. More generally, those skilled in the art will readily appreciatethat all parameters, dimensions, materials, and configurations describedherein are meant to be an example and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the inventive teachingsis/are used. Those skilled in the art will recognize, or be able toascertain using no more than routine experimentation, many equivalentsto the specific inventive embodiments described herein. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto, inventive embodiments may be practicedotherwise than as specifically described and claimed. Inventiveembodiments of the present disclosure are directed to each individualfeature, system, article, material, kit, and/or method described herein.In addition, any combination of two or more such features, systems,articles, materials, kits, and/or methods, if such features, systems,articles, materials, kits, and/or methods are not mutually inconsistent,is included within the inventive scope of the present disclosure. Someembodiments may be distinguishable from the prior art for specificallylacking one or more features/elements/functionality (i.e., claimsdirected to such embodiments may include negative limitations).

Also, various inventive concepts may be embodied as one or more methods,of which an example has been provided. The acts performed as part of themethod may be ordered in any suitable way. Accordingly, embodiments maybe constructed in which acts are performed in an order different thanillustrated, which may include performing some acts simultaneously, eventhough shown as sequential acts in illustrative embodiments.

Any and all references to publications or other documents, including butnot limited to, patents, patent applications, articles, webpages, books,etc., presented anywhere in the present application, are hereinincorporated by reference in their entirety. Moreover, all definitions,as defined and used herein, should be understood to control overdictionary definitions, definitions in documents incorporated byreference, and/or ordinary meanings of the defined terms

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of,” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “tholding,” “composed of,” and the like areto be understood to be open-ended, i.e., to mean including but notlimited to. Only the transitional phrases “consisting of” and“consisting essentially of” shall be closed or semi-closed transitionalphrases, respectively, as set forth in the United States Patent OfficeManual of Patent Examining Procedures, Section 2111.03.

The invention claimed is:
 1. A signal separation system for distinguishing between at least a first type of charged particle and a second type of charged particle emitted from a specimen, comprising: a convertor assembly comprising: at least a first layer configured to emit, in response to impingement of the first type of charged particle on the first layer, a first signal containing a first type of image information; and a second layer configured to emit, in response to impingement of the second type of charged particle on the second layer, a second signal containing a second type of image information, the first and second signals are emitted as a combined signal from the convertor assembly; and a signal separator assembly configured to receive the combined signal and separate the first signal from the second signal.
 2. A signal separation system according to claim 1, wherein the first signal is emitted at a first predetermined wavelength and the second signal is emitted at a second predetermined wavelength.
 3. A signal separation system according to claim 1, wherein the convertor assembly comprises a multilayer scintillator assembly comprising the first layer which includes a first scintillating layer and the second layer which includes a second scintillating layer.
 4. A signal separation system according to claim 1, wherein the first type of charged particle comprise at least one of secondary electrons (SEs) and secondary ions (SIs) and the second type of charged particle comprise at least one of backscattered electrons (BSEs) and backscattered ions (BSIs).
 5. A signal separation system according to claim 1, wherein the first and second signal are received synchronously by the signal separator.
 6. A signal separation system according to claim 1, wherein following separation of the first signal from the second signal by the signal separator, the separated first signal is directed to a first image processor for producing a first image containing the first image information and the separated second signal is directed to a second image processor for producing a second image containing the second image information.
 7. A signal separation system according to claim 6, wherein the first image and the second image show image information captured synchronously.
 8. A signal separation system according to claim 1, wherein the signal separation system is positions within a microscopy system.
 9. A method for separating signals for distinguishing between at least a first type of charged particle and a second type of charged particle emitted from a specimen, comprising: irradiating a specimen with a primary beam for emitting at least the first type of charged particle and the second type of charged particle; impinging a first layer of a convertor assembly configured to emit, in response to impingement of the first type of charged particle on the first layer, a first signal containing a first type of image information; impinging a second layer of the convertor assembly configured to emit, in response to impingement of the second type of charged particle on the second layer, a second signal containing a second type of image information, wherein a combined signal comprising the first and second signal emits the convertor assembly; receiving the combined signal by a signal separator assembly; and separating the combined signal by the signal separator assembly into at least the first signal and the second signal.
 10. A method for separating signals according to claim 9, wherein the separated first signal is amplified by a first photomultiplier and processed to provide an image containing the first type of image information and the separated second signal is amplified by a second photomultiplier and processed to provide an image containing the second type of image information. 